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Walking lessons from orangutans

In the typical picture of human evolution, a gorilla- or chimp-like ape, dragging its knuckles on the ground, gradually straightens up and turns into a modern human standing on two legs.

A group of scientists in the United Kingdom now has a different idea for how we came to walk on two legs. They got their idea from watching wild orangutans, who spend almost their whole lives in the trees of the rainforest (partly to avoid tigers who are licking their lips at the thought of dining on an orangutan.)

Dr. Susannah Thorpe of the University of Birmingham and her colleagues noticed that orangutans often walk through the trees on two legs, using their arms to hold onto other branches for balance.

When they watched more closely, the researchers found that the orangutans used this walking style the most when they were venturing on to thin, flexible branches, which is usually where the best fruit is.

The early ancestor to orangutans, chimps, gorillas and humans also lived in the trees, the way orangutans do today.

Dr. Thorpe and her colleagues think that these ancestors may have also walked upright in the trees, and that this would have helped them travel along thin branches to pick fruit.

Eventually, these ancestor apes came down from the trees. Some stayed on the ground and continued to walk on two legs, and modern humans may have eventually evolved from this group.

Chimps, gorillas and other modern-day apes may have evolved from different groups of ancestors who didnít leave the trees altogether but instead became adapted to climbing up and down.

The scientists describe their research in the 1 June issue of the journal Science.